1. Field of the Invention
The invention relates to processes to reduce or even prevent the formation of spots on the over wrapper of cigarettes as well as the paper used in such processes and the resulting cigarettes.
Cigarettes are generally wrapped in white cigarette paper. The degree of whiteness of a cigarette is considered as an indication of quality. Conversely, yellowing or the presence of brown spots on a cigarette paper is considered by consumers as a sign of poor quality or the cigarettes having been too long in storage. Experts know, however, that extended storage is not a prerequisite to yellowing or spotting. In fact, when cigarettes are kept under high humidity, spotting may occur within weeks or even days.
Spotting is explained by the transfer, at the point of contact between tobacco shreds and cigarette paper, of tobacco-colored constituents. Cigarette paper is a highly hydrophilic material, due to (i) the chemical nature of cellulose, with its large number of hydroxyl groups, (ii) the physical structure of the fibers presenting a microcapillarity and (iii) the porous structure of the sheet (see N. Baskevitch, Annales du Tabac (Paris) vol. 14, pp 33-43 (1976)).
Under the influence of high relative humidity, tobacco constituents transferred to the internal face of cigarette paper migrate through the paper to form visible discrete spots on the outside of the wrapper. No technique exists today which allows to solve a spotting problem when cigarettes are stored in extreme climatic conditions.
The object of the invention is to propose a technique allowing to solve this problem.